N-(dihydrocarbylphosphorodithio)imides as premature vulcanization inhibitors

ABSTRACT

A method for inhibiting the premature vulcanization of rubber compounds comprising the incorporation in a rubber mix a compound having the formula   WHEREIN R1 and R2 are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to 16 carbon atoms and may be interconnected to form a cyclic compound and wherein R3 and R4 are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to 16 carbon atoms.

United States Patent [1 1 Lohr, Jr. et al.

[451 Feb. 11, 1975 N-(DIIIYDROCARBYLPI-IOSPHORODITI-II- O)IMIDES AS PREMATURE VULCANIZATION INHIBITORS [75] Inventors: Delmar F. Lohr, Jr.; Edward L.

Kay, both of Akron, Ohio [73] Assignee: The Firestone Tire & Rubber Company, Akron, Ohio 221 Filed: Aug. 31, 1973 211 App]. No.: 393,517

Yaucher et a1 260/79.5 B

FOREIGN PATENTS OR APPLICATIONS 164,670 8/1964 U.SIS.R 260/780 Primary Examiner-Melvyn L. Marquis Assistant Examiner-Gary R. Marshall [57] ABSTRACT A method for inhibiting the premature vulcanization of rubber compounds comprising the incorporation in a rubber mix a compound having the formula wherein R, and R are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to 16 carbon atoms and may be interconnected to form a cyclic compound and wherein R,, and R are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to 16 carbon atoms.

8 Claims, N0 Drawings 1 N-(DIHYDROCARBYLPHOSPHORODITHIO)I- MIDES AS PREMATURE VULCANIZATION INHIBITORS BACKGROUND, OF THE INVENTION crease output of the curing equipment. Example of such retarders are set forth in U.S. Pat. Nos. 3,539,538; 3,546,185; and 3,562,225.

The compounds of the present invention relate to a new class of premature vulcanization inhibiting compounds which retard the start of cure in a rubber mix and also increase the cure rate. Heretofore, such compounds were never used in the rubber compound field although a similar class of compounds, U.S. Pat. No. 2,995,568, have been solely used as pesticides to control flies and spider mites.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a new group of premature vulcanization inhibitors.

It is a further object of the present invention to provide a group of premature vulcanization inhibiting compounds, as above, which retard vulcanization at a specific temperature range.

It is a still further object of the present invention to provide a group of premature vulcanization inhibiting compounds, as above, which increase scorch delay and the crosslinking rate in the vulcanization of rubber mixes.

These and other objects of the present invention are described in detail without attempting to discuss all of the various modifications in which the invention might be embodied; the invention being measured by the appended claims and not by the details of the specification.

In general, a method of inhibiting premature vulcanization in rubber mixes relates to the application to the rubber mix a compound as in the formula wherein R R R and R are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to 16 carbon atoms and wherein R and R may be interconnected to form a cyclic compound.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Compounds of the present invention which inhibit premature vulcanization can generally be classified as N-(dihydrocarbylphosphorodithio) imides. More specifically, these compounds are represented by the .formula wherein R, and R are aliphatic, cyclic, aromatic hydrocarbon groups or mixtures thereof containing from 1 to about 16 carbon atoms. Moreover, R and R may be interconnected, that is a portion of a cyclic compound so that together with an imide group is formed. R and R may also be ali phatic, cyclic, aromatic hydrocarbon groups or mixtures thereof-containing from 1 to about 16 carbon atoms and preferably from 1 to 10 carbon atoms. Of course, the aliphatic compounds may be branched.

These compounds may be used with any rubber mixture such as for tire tread,'tire body, rubber molding, and the like, wherein the rubber mixture contains a sulfur curative system. Generally, the amount of the inhibitor ranges from 0.05% to about 5% based solely upon the rubber compound in the rubber mixture. A more desirable range is from 0.1% to about 1.0%.

The N-(dihydrocarbylphosphorodithi0)imide compounds of the present invention can be prepared in an inert solvent such as tetrahydrofuran ambient temperatures and normal pressures as indicated by the following equation wherein R R R R are as set forth above and wherein X is a halogen atom, preferably chlorine or bromine, and M is a group 1A metal ion, preferably sodium or potassium.

Representative examples of N-(dihydrocarbylphosphorodithio)imides which are preferred in the present invention due largely to ease of preparation include:

N-(dimethylphosphorodithio) succinimide N-(diethylphosphorodithio) succinimide N-(diisopropylyphosphorodithio) succinimide N-(di-n-octylphosphorodithio) succinimide N-(di-2-ethylhexylphosphorodithio) succinimide N-(dicyclohexylphosphorodithio) succinimide N-(diphenylphosphorodithio) succinimide N-(ditolylphosphorodithio) succinimide 3 N-(dinaphthylphosphorodithio) succinimide N-(dimethylphosphorodithio) phthalimide N-(diethylphosphorodithio) phthalimide pm by N-(diisopropylphosphorodithio) phthalimide Styrene/butadiene copolymer 100 N-(di-n-octylphosphorodithio) phthalimide 22 black 33 N-(di-2-ethylhexylphosphorodithio) phthalimide Zinc pm; 2 N-(dicyclohexylphosphorodithio) phthalimide g i Held U U! N'(dfphenylphosphol9duhlo) phthalimide N-Tert. butyl-Z-benzothiazolesulfenamide 1.4 N-(dltolylphosphorodlth1o) phthalimide and N-(l,3-Dimethy1butyl)-l}1-phenyl- 1.0 N-(dinaphthylphosphorodithio) phthalimide 1O p'phenylened'amme Although, the above representative examples set forth the use of the various succinimides, and hthalimides groups other dicarboximides compouiids de- The styreneibutadlene c-opolymer rubber mixture was prepared in a conventional hydrocarbon solvent 12:3 2x3 2222 5 i gg i i q l 5 such as hexane with a alkyllithium initiator. The rubber lutarimides maleir id es an d iia hthi li iilzs r r i zi al s o mixture Contained usual or typical processus d p y ing oil, carbon black, zinc oxide, stearic acid, sulfur, 'remature vulcanization inhibitors ma b Sed antioxidant and a sulfenamide accelerator. This rubber to revim crosslinkin at low or nomcurin uera mixture was blended and the following amounts of varip g g p ous inhibitors according to the present Invention were tures of generally any type of rubber mixture contamdd d f T b] 1 Th bb ing a rubber compound such as polybutadiene, polyse on a e m er z a were tyrenebutadiene rubber, polyisoprene, nitrile rubbers, t en if e 3 a l an i polyisobutylene, polychloroprene, and the like and vari. as we as e 6 ere e mi ious amounts of oil, carbon black, and the like. That is, Addmopany the elasticlty and the ummaie during any conventional operation such as preparation i gg fi were also determined and are Set forth m of a master batch, storage or the lke, the inhibitors will 6 retard the formation of premature vulcanization which TABLE 1 often renders processing of the rubber such as for calendering or extruding or shaping a tire, impractical TestStock 1 2 3 4 5 6 7 since the occurrance of crosslinking renders the rubber 5 12 rough and lumpy. Moreover, the present inhibitors php of: have been found to increase scorch delay and unlike Sample A 0.2 prior art retarders, generally do not significantly reduce sample B 0,2 the cure rate or rate of crosslinking the rubber com- Samplec 01 pound upon actual cure Long scorch times are desirg i g 'j'fg fi fi g fi a g f d ampe is iiscpropyp asp are it iolp t aimi e. able not only for safety reasons, but also for quicker or Sample c is N-(dicyclohexylphosphorodithio)succinimide.

TABLE 11 Monsanto Rheometer, 300F, 1 Are, 100 rpm. Mini Die Scorch Time, Minutes 13.6 14.1 15.3 12.2 13.3 13.4 14.3 Time to Optimum (90%) Cure. Minutes 23.5 21.0 22.4 18.2 18,1 18.2 19.0 Cure Rate Index* 10.1 14.5 14.1 16.7 20.8 20.8 21.3

Normal Stress-Strain. Cured 23 at 300F 300% Modu1us.psi 1160 1511) 1575 1350 1325 1450 1325 Ultimate Elongation.

605 500 440 540 490 530 500 Tensile, psi 3160 2975 2600 3050 2725 3275 2775 Cure Rate Index is defined as 100/(Time to Optimum Cure-Scorch Time).

shorter time periods required for optimun cure. Hence, From Table 11, it is readily apparent that phthalimide production output on existing curing equipment can be inhibitors A and B gave higher scorch times than the increased. Additionall the increase crosslinkin rate control which did not contain an inhibitor. Also the y g y or tighter cure affects the physical properties of the time required to optimum cure on test stocks 2 and 3 rubber compound as, for example, increasing the elaswere also lower than the control. Thus, the cure rate ticity modulus and decreasing the ultimate elongation. index which is defined as 100 divided by the time to op- In order to test the effect of the N- timum cure minus the scorch time was considerably (dihydrocarbylphosphorodithio)imides, a styrenelhigher for stocks 2 and 3. Considering now test stocks butadiene copolymer rubber mixture was prepared according to the following recipe:

RECIPE FOR A RUBBER MIXTURE 5, 6 and 7 which contained a succinimide inhibitor, as compared to the control, test stock number 4, the

scorch time in these series of tests were also increased and thus the cure rate index was substantially higher.

Considering the stress strain data, for each series bf tests, the modulus was generally higher and the elonga tion was significantly lower than the control stocks, The physical date values are indicative of a tight cure.

It can thus be seen that the disclosed invention carries out the objects of the invention set forth above. As will be apparent to those skilled in the art, many modifications can be made without departing from the spirit of the invention herein disclosed and described, the scope of the invention being limited solely by the scope of the attached claims.

What is claimed is:

l. A method of inhibiting premature vulcanization in rubber compounds comprising applying to rubber compounds selected from the class consisting of polybutadiene, polystryenebutadiene, polyisoprene, nitrile rubbers,and polychloroprene an inhibitor wherein R, and R are aliphatic, cyclic or aromatic hydrocarbon groups or mixtures thereof containing from 1 to about 16 carbon atoms, said R, and R are interconnected and taken together with said group to form an imide group, i

and wherein R and R are aliphatic, cyclic, or aromatic hydrocarbon groups or mixtures thereof containing from 1 to about 16 carbon atoms, and said inhibitor ranging from about 0.05% to about 5.0% by weight of said rubber compound.

4. A method of inhibiting premature vulcanization as in rubber compounds comprising applying to rubber compounds selected from the class consisting of polybutadiene, polystyrenebutadiene, polyisoprene, nitrile rubbers, and polychloroprene N-(dihydrocarbylphosphorodithio)imide inhibitors wherein said imides are selected from the class consisting of phthalimides and succinimides and said inhibitor ranging from about 0.05% to about 5.0% by weight of said rubber compound.

5. A method of inhibiting premature vulcanization as in claim 4, wherein said hydrocarbyl groups have from 1 to about 16 carbon atoms.

6. A vulcanizable composition comprising a rubber compound selected from the class consisting of polybutadiene, polystyrenebutadiene, polyisoprene, nitrile rubbers, and polychloroprene,

a premature vulcanization inhibitor having the forwherein R, and R are aliphatic, cyclic, or aromatic hydrocarbon groups or mixtures thereof containing from 1 to about 16 carbon atoms, said IR, and R are interconnected and taken together with said group to form an imide group,

and wherein R and R are aliphatic, cyclic, or aromatic hydrocarbon groups or mixtures thereof containing from 1 to about l6 carbon atoms, and

said inhibitor ranges from about 0 .05% to about 5.0%

by weight of said rubber compound.

7. A vulcanizable composition as in claim 6, wherein said imides are selected from the group consisting of phthalimides, succinimides, adipimides, glutarimides, maleimides, and naphthalimides.

8. A vulcanizable composition as in claim 6, wherein R and R ranges from 1 to about [0 carbon atoms. 

1. A METHOD OF INHIBITING PREMATURE VULCANIZATION IN RUBBER COMPOUNDS COMPRISING APPLYING TO RUBBER COMPOUNDS SELECTED FROM THE CLASS CONSISTING OF POLYBUTADIENE, POLYSTRYENEBUTADIENE, POLYISOPRENE, NITRILE RUBBERS, AND POLYCHLOROPRENE AN INHIBITOR
 2. A method of inhibiting premature vulcanization, as in claim 1, wherein said imides are selected from the class consisting of phthalimides, succinimides, adipimides, glutarimides, maleimides, and naphthalimides.
 3. A method of inhibiting premature vulcanization as in claim 1, wherein R3 and R4 range from 1 to about 10 carbon atoms.
 4. A method of inhibiting premature vulcanization as in rubber compounds comprising applying to rubber compounds selected from the class consisting of polybutadiene, polystyrenebutadiene, polyisoprene, nitrile rubbers, and polychloroprene N-(dihydrocarbylphosphorodithio)imide inhibitors wherein said imides are selected from the class consisting of phthalimides and succinimides and said inhibitor ranging from about 0.05% to about 5.0% by weight of said rubber compound.
 5. A method of inhibiting premature vulcanization as in claim 4, wherein said hydrocarbyl groups have from 1 to about 16 carbon atoms.
 6. A vulcanizable composition comprising a rubber compound selected from the class consisting of polybutadiene, polystyrenebutadiene, polyisoprene, nitrile rubbers, and polychloroprene, a premature vulcanization inhibitor having the formula
 7. A vulcanizable composition as in claim 6, wherein said imides are selected from the group consisting of phthalimides, succinimides, adipimides, glutarimides, maleimides, and naphthalimides.
 8. A vulcanizable composition as in claim 6, wherein R3 and R4 ranges from 1 to about 10 carbon atoms. 